1. Technical Field
The invention generally relates to switch mode power supplies. More particularly, the invention relates to switch mode power supplies that are current controlled to maintain a substantially constant line current at an optimized power factor.
2. Related Art
As the power capability of a power converter, or power supply, grows, the need to better utilize the power source follows close behind. The distribution of power throughout the world has coalesced on a sinusoidal AC network leading to the advent of power factor corrected processing. Prior developed power factor correction or PFC stages have used a two-stage boost based converter, or a single stage converter to achieve the voltage requirements for a load on the power supply and to achieve galvanic isolation.
In prior art PFC stages, the line current supplied is subject to substantial changes in magnitude due to the sinusoidal nature of the line voltage and current and a typically varying load. In order to achieve unity power factor, the peak current should occur substantially in phase with the peak voltage. As a result, the PFC stage switches the highest current and the highest voltage at the same time. Due to the high magnitude of current drawn during peak and valley voltages, the number and/or robustness of the switching devices are increased. In addition, higher stresses on the switching devices may be experienced during operation. These factors tend to increase cost, reduce longevity and reduce overall efficiency of the power converter. Overall efficiency can be compromised by energy loss and accompanying buildup of heat that accompanies such high magnitude current and voltage switching.